Early detection and treatment of breast cancer have improved survival, consequentially increasing a potentially serious complication called lymphedema. Lymphedema, characterized by painful swelling of the arm, affects 3- 60% of breast cancer survivors, leading to disability and reduced quality of life. A recent NCI Cancer Bulletin reported that many cancer survivors are unaware that they are afflicted with lymphedema, suggesting that lymphedema rates are underestimated. This may explain the wide variation in reported rates. We propose to conduct a population-based study to address the limitations posed by previous studies including their failure 1) to examine subclinical or non-physician-diagnosed lymphedema, 2) to evaluate the role of upper extremity exercise, and 3) to consider the role of co-morbidities. Our population-based study will target 815 female breast cancer survivors, identified through the Iowa Cancer Registry (ICR), diagnosed during 2003 with a first primary invasive cancer at localized or regional stage. Suspected etiology factors will be self-reported via a computer-assisted telephone interview or from ICR. We will define chronic lymphedema as physician-diagnosed or subclinical cases as follows: 1) Physician diagnosed cases only 2) Subclinical cases based on objective measure (>2 cm difference in arm circumferences) 3) Subclinical cases defined by either objective or subjective self reported symptoms. This will include subjects with >2cm difference between arm circumference (objective) or those who answered positively to arm symptoms (subjective). Comparison of these 3 definitions will help us determine if a large number of potential cases are going undiagnosed and if such differences may explain the variation in incidence rates previously reported. The specific aims of this application include: 1) Developing a lymphedema questionnaire that estimates the extent of subclinical lymphedema cases. 2) Estimating the incidence of chronic lymphedema (physician diagnosed, subclinical cases based on objective symptoms alone, subclinical cases based on both objective and subjective symptoms) and describing the variation of incidence rates due to follow-up times and lymphedema definitions. 3) Examining lymphedema risk factors, including upper extremity exercise and obesity. The goal of the proposed project is to identify modifiable factors that prevent lymphedema among survivors.